The mold, Botrytis cinerea, is found in all wine growing regions. This fungus infects the grapes whereby their skin becomes covered by the mold, the interior of the grape providing nutriment via the fungal mycelium. The infestation leads to a loss of water in the grape which causes the grape to shrink and concentrate the contents therein. In some regions the infestation by the mold is actively supported and eagerly sought by the wine grower because the resulting wines are generally considered to be of outstanding quality. This applies to, for example, all types of Spatlese, Sauternes, Hungarian Tokay and others.
However, the handling of musts and wines from Botrytis infected grapes usually confronts the wineries with technical obstacles in that they are more difficult to filter than those from non-infected grapes. Indeed, filtration takes substantially more time and may use as much as five to ten times more filter plates than is the case with a normal wine.
Recent investigations have revealed that the filtration difficulty is attributable to a glucan formed by the fungus, the glucan being present as a colloid in the must and in the wines fermented from the Botrytis infected grapes, in relatively small concentration, usually of the order of 5-400 mg per liter. Structurally, this glucan has been reported to be a beta-glucan with a 1,3-beta-glucan main chain and 1,6-beta-linked side chains. The average molecular weight is about 1 million Dalton. Although other types of colloid material are known to be present in wine in approximately the same weight proportion e.g., 200-700 mg/l, the filtration difficulty is believed to be almost entirely attributable to the above described beta-glucan.
As might perhaps be expected, once the filterability problem was attributed to the presence of a beta-glucan, workers in the art investigated the action of a large number of available beta-glucanases and cellulases on wines and musts from Botrytis infected grapes without, however, any noticeable degree of sucess. Thus, when testing such typical beta-glucanases as CEREFLO.RTM. and FINIZYM.RTM., obtained from Bacillus subtilis and Aspergillus niger, respectively, the inventor hereof failed to observe any noticeable improvement of filtration rate, and similar negative results were found with CELLUCLAST.RTM., a cellulase originating from Trichoderma reesei. (The proprietary enzymes were supplied by NOVO INDUSTRI A/S, Denmark.)
The object of this invention is to provide an enzymatic treatment process that improves the filterability of musts and wines produced from Botrytis infected grapes.